GGA+U study of the electronic and optical properties of hexagonal BN phase ZnO under pressure

• GGA+U method is more suit for strongly correlated ZnO.
• Band gap and α(ω) of Bk phase versus pressure were fitted by linear equations.
• Changes in optical properties (B4 and Bk) at PTr have been discussed.
• Relations between band, optical properties and DOS have been discussed.
• Our study is significant in optics, material science, physics and geology.

We used the CASTEP program with a GGA+U method to study the electronic and optical properties of BN (Bk) phase ZnO under pressure. At transition pressure, the properties of Bk phase have been compared with those of wurtzite (B4) phase ZnO. The BN phase has been predicted recently. The GGA+U method can provide an accurate band gap, which is more suit for strongly correlated ZnO. The calculated band gap shows BN phase is an insulator. The band gap increases with increasing pressure. The increasing band gap induces a blue-shift optical properties. A linear equation was used to fit the relation between band gap and pressure. The dielectric function (ε(ω) = ε1(ω) + ε2(ω)) has been calculated. The relations between ε2(ω) and density of states have been discussed. The other optical constants have also been calculated. The relation between absorption coefficient (α(ω)) and pressure was also fitted by another linear equation. The linear equation about α(ω) can be used to measure pressure. The optical constants show Bk phase ZnO is transparent. Our study can be used to identify the BN phase and some geological processes. Our calculations also provide theoretical data for potential applications of BN phase ZnO in the future.

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